The invention relates to a tubular capacitor. Such capacitors are known and, as a rule, consist of a tube or sleevelike element produced from ceramic, on whose outside peripheral surface and inside surface layers of electrically conductive material, namely metal layers are applied so that the two galvanically separated capacitor coatings are obtained.
But in the case of these known tubular capacitors it is disadvantageous that they exhibit only a small mechanical loading capacity because of the use of the sleevelike element forming the dielectric, i.e., the sleevelike element easily breaks, which raises great problems, especially in the case of contacting, i.e., in the case of attachment of contact surfaces or leads necessary for later insertion of the capacitor in an electric circuit. Contacting also in tubular capacitors recently has often taken place with the help of metal caps, on which in each case, in the formation of the tubular capacitor, a lead is connected, electrically conductive, with one end as component provided with leads. But it is also possible to provide the metal caps without leads, so that the metal caps themselves are used as leads in the later insertion of the capacitor in an electric circuit. In this case, these capacitors are then identified as "MELF tubular capacitors".
For contacting of the metal layer applied on the outside peripheral surface of the sleevelike element and forming the first capacitor coating, one of the two metal caps, designed cuplike, is put on the one end of the sleevelike element, so that this metal cap, by its peripheral wall forming the cup shape, rests electrically conductive against the metal layer applied to the outside peripheral surface. For contact between the metal layer provided on the inside surface of the sleevelike element and the metal layer forming the second capacitor coating it is necessary in these known tubular capacitors to make the metal layer forming the second capacitor coating so that it extends on the other end of the sleevelike element up to the outside peripheral surface of this element and forms a contacting surface there, which is galvanically separated from the first capacitor coating and rests, electrically conductive, against the peripheral wall of the second metal cap forming the cup shape. Already for this fact along the production of the two metal layers is expensive. But because of the slight strength of the sleevelike element it is not possible to fasten the metal caps on the sleevelike element by force fit but a soldering connection between them and the respective metal layer is necessary for holding the metal caps. This also means an additional production engineering expense, especially since the use of automatic capping machines, such as used in the production of other components (e.g., resistors), is not possible. Moreover, because of the above-mentioned soldering connections it is not possible, after capping of the sleevelike element, to fasten leads to the metal caps by welding, rather the metal caps already provided with leads must be applied to the sleevelike element, which also raises considerable production engineering problems.
The object of the invention is to show a tubular capacitor which exhibits considerably improved mechanical strength and also makes possible a simplified production.
To achieve this object, a tubular capacitor of the type initially described is designed according to the characterizing part of claim 1.
Because in the sleevelike element forming the dielectric of the capacitor there is inserted, in a matching manner, a core with at least one section, which for formation of the second capacitor coating is designed electrically conductive in at least one partial area of the peripheral surface, for the tubular capacitor a solid component body, formed from a sleevelike element and from the section of the core placed in it, is achieved, which exhibits a high mechanical strength, so that especially there is no danger that this component body will be broken or crushed by the action of outside force. In this way it is possible to use metal caps for the contacting which are held by force fit or by pressing together firmly or pressing on the sleevelike element.
Since the second capacitor is formed from an electrically conductive layer on an outside surface, namely on the peripheral surface of the core, achievement of this second capacitor coating is considerably simplified.
In the preferred embodiment of the invention the core is designed so that with another section, whose outside diameter preferably is equal to the outside diameter of the sleevelike element, it projects over the other side of the sleevelike element, and the core at least on the peripheral surface of this other section is also made electrically conductive and the contact surface of the second capacitor coating is formed there so that here the contacting also takes place with the help of metal cap held by force fit. Capping of the tubular capacitor according to the invention can take place with the help of metal cap held by force fit. Capping of the tubular capacitor according to the invention can be used either as a MELF tubular capacitor or leads can be fastened by welding on the metal caps of the capped tubular capacitor.